That's a pretty long list and I probably should be in bed right now...
1) Yes, the Deneb will at least run in PIO mode. If you deactivate other busmasters (e.g. the SCSI controller), you normally can also operate it in DMA mode. If you encounter freezes or crashes with the DMA driver, you should fall back to PIO mode.
The PIO mode will suck as much CPU time that is available and necessary to read data from or write data to the USB medium. So given you want to copy data from a fast source (e.g. memory) to a USB stick which can handle that speed, you probably will end up with >90% CPU usage.
Regarding USB audio, the usage is probably less than 5%, not including audio mixing and processing (mp3 decoding) that is done by AHI for any kind of soundcard.
For networking, it largely depends on the TCP/IP stack, which usually is the CPU bottleneck -- no different than other Zorro based ethernet cards, except for Zorro III bus access being a lot faster than the available Zorro II boards and 100MBit/s having less latency than the 10MBit/s cards.
As for the DMA mode not being available under OS4: The OS4 new memory model needs hardware to support scatter/gather rather than linear addressing. The current Deneb firmware does not support this right now. While it is possible to add a software workaround for this (with moderate efforts), smaller DMA blocks and more calls to CachePreDMA() and CachePostDMA() would probably kill the effectiveness of the DMA routines for less than 1% of the users. Given this ratio, the PIO driver seems to be a legit fallback for OS4.
BTW: I don't consider the DMA driver to be broken under OS4. In fact, it will use DMA whenever linear memory transfers are encountered and only fall back to PIO automatically when scatter/gather would have been required. However, it needs correct implementations of CachePreDMA() and CachePostDMA(). Unfortunately, currently for unknown reasons the driver still seems to freeze the machine under OS4. It could be that this is due to a bug in the said routines in OS4 (which have been proven broken in earlier versions).
I think users of
www.a1k.org/forum have done some benchmarking under OS4, maybe APeX has information about the CPU usage. I guess they should be more or less than same.
2) The Deneb flash can be used to directly boot into MorphOS without prior reboots. The instructions on how to install MorphOS into the flashrom are covered in the Luciferin manual (you can download the SW from my homepage).
As I don't have a Zorro III capable PPC machine (only an A1200PPC), I couldn't do any speed tests for DMA driven MorphOS. The PPC-native distribution of Poseidon for MorphOS Classic PUP is still pending. I hopefully will be able to provide it within this week.
3) As for reliability, probably other users should speak up. As for me, I'm using the Deneb (Zorro II after the breakdown of my A4000T) for at least keyboard, mass storage and networking for several months now and it hasn't failed me once.
4) Updates to the DMA engine (firmware) have been proposed, but due to the small number of users the massive changes necessary have not been considered for implementation yet. Indeed, if CachePreDMA() and CachePostDMA() are still broken in OS4, changes of the DMA engine would be moot.
Phew. I hope this answers your questions
